A theoretical physicist explains why the hard problem in science today is not about physics at all

When you stop at a red light, you probably don't give much thought to it. You see red and you know to hit the brakes.

It's a useful concept, theoretical physicist Sean Carroll says in his book "The Big Picture: On the Origins of Life, Meaning, and the Universe Itself." The stoplight can be recognized universally and objectively by those capable of seeing color without restrictions.

But when it comes to seeing red, there's more to it than meets the eye.

One of the hardest questions in science, Carroll says, has to do with something called qualia, which is the subjective experience of the way something seems to us.

Do you and I see the same thing when we see the color red? What is it like to experience the redness of the light? This is what Carroll calls 'the hard question.'

It's the type of question that transcends the physical world. It can't be answered purely in terms of physical behavior. It can't be accounted for simply by the motion of unthinking matter.